The present invention relates to an apparatus and method for check weighing material contained in a container which is passing along a production line. The invention particularly relates to the use of magnetic resonance techniques for such check weighing.
In today""s industrial environment there is a continuous need to improve efficiency, quality and yield. As a result, automated control and quality assurance (QA) systems for manufacturing lines are becoming increasingly important. One type of monitoring device commonly used on product filling lines is a check weighing device, which is used to ensure that the required amount of product is put in each container.
As one example, check weighing is used by the pharmaceuticals industry for the monitoring and regulation of the amount of a drug in a sealed glass vial during filling. The drug weight can be as small as a fraction of a gram, and is required to be weighed with an accuracy of a few per cent or better, in a vial weighing tens of grams at a rate of several weighings per second. At present, to obtain the required accuracy, it is necessary to remove the vials from the production line and to weigh them on precision balances. This must be done both before and after filling in order to take into account the weight of the container. Inevitably this is a time consuming process and 100% inspection cannot be achieved while maintaining throughput. As a result only a fraction of the product is ever tested. Therefore, if something does go wrong and the vials are not being filled with the correct amount of the drug, then a large batch of product can be wasted before the problem is even noticed. Furthermore, since the vial must be weighed both before and after filling, the weighing must be performed in the aseptic environment between filling and sealing.
The present invention aims to provide an alternative technique for check weighing products on a production line.
This and other objects are attained in accordance with one aspect of the invention directed to an apparatus for determining an on-line measure of the mass of each of a plurality of discrete samples in a production line. The apparatus includes a transporter operable to transport the plurality of discrete samples along a transport path through an interrogation zone. A static magnetic field generator is operable to generate a static magnetic field in a first direction through the interrogation zone for creating a net magnetisation within a current sample located within the interrogation zone. An alternating magnetic field generator is operable to apply a pulse of alternating magnetic field in a second different direction through the interrogation zone for temporarily changing the net magnetisation of the current sample located within the interrogation zone. A position sensor is operable to sense the position of each discrete sample on the transporter as it approaches the interrogation zone and operable to output a corresponding position signal. A controller is operable to control the timing of the application of the pulse of alternating magnetic field by the alternating magnetic field generator in dependence upon the position signal output by the position sensor so that the pulse of alternating magnetic field is applied when the current sample is in the interrogation zone. A sensor is operable to sense energy emitted by the current sample as the net magnetisation of the current sample returns to its original state and operable to output a sensor signal in dependence thereon. Processing circuitry is operable to process the sensor signal to determine a measure of the amplitude of the energy emitted by the current sample. A memory is operable to store predetermined calibration data defining a relationship between the amplitude measure and mass, which calibration data is obtained from an amplitude measure determined by the processing circuitry for one or more similar samples of known mass. A measuring device is operable to determine the measure of the mass of the current sample using the calibration data and the amplitude measure output by the processing circuitry for the current sample. The static magnetic field generator is operable to generate a static magnetic field which is substantially homogeneous over a length of the transport path so that each sample is exposed to the static magnetic field for a predetermined period of time before it reaches the interrogation zone.
Another aspect of the invention is directed to a method of determining an on-line measure of the mass of each of a plurality of discrete samples in a production line. The method includes transporting the plurality of discrete samples along a transport path through an interrogation zone, generating a static magnetic field in a first direction through the interrogation zone to create a net magnetisation within a current sample located within the interrogation zone, applying a pulse of alternating magnetic field in a second different direction through the interrogation zone to temporarily change the net magnetisation of the current sample located within the interrogation zone, and sensing the position of each discrete sample along the transport path as it approaches the interrogation zone and outputting a corresponding position signal. The method further includes controlling the timing of the application of the pulse of alternating magnetic field in dependence upon the position signal output in the position sensing step, so that the pulse of alternating magnetic field is applied when the current sample is in the interrogation zone, sensing energy emitted by the current sample as the net magnetisation of the current sample returns to its original state and outputting a sensor signal in dependence thereon, processing the sensor signal to determine a measure of the amplitude of the energy emitted by the current sample, storing predetermined calibration data defining a relationship between the amplitude measure and mass, which calibration data is obtained from an amplitude measure determined in the processing step for one or more similar samples of known mass, and determining the measure of the mass of the current sample using the calibration data and the amplitude measure output by the processing step for the current sample. The generating step generates a static magnetic field which is substantially homogeneous over a length of the transport path so that each sample is exposed to the static magnetic field for a predetermined period of time before it reaches the interrogation zone.
Yet another aspect of the invention is directed to a method of producing sealed containers containing a predetermined amount of a sample. The method includes filling the container with the predetermined amount of sample, sealing the sample within the container, transporting each of the filled containers along a transport path to a weighing station, weighing the sample within each of the containers, and rejecting any containers which do not contain the predetermined amount of sample within a predetermined tolerance. The weighing is accomplished by generating a static magnetic field in a first direction through an interrogation zone to create a net magnetisation within a sample located within the interrogation zone, applying a pulse of alternating magnetic field in a second different direction through the interrogation zone to temporarily change the net magnetisation of the current sample located within the interrogation zone, sensing the position of each discrete sample along the transport path as it approaches the interrogation zone and outputting a corresponding position signal, controlling the timing of the application of the pulse of alternating magnetic field in dependence upon the position signal output in the position sensing step, so that the pulse of alternating magnetic field is applied when the current sample is in the interrogation zone, sensing energy emitted by the current sample as the net magnetisation of the current sample returns to its original state and outputting a sensor signal in dependence thereon, processing the sensor signal to determine a measure of the amplitude of the energy emitted by the current sample, storing predetermined calibration data defining a relationship between the amplitude measure and mass, which calibration data is obtained from an amplitude measure determined in the processing step for one or more similar samples of known mass, and determining a measure of the mass of the current sample using the calibration data and the amplitude measure output by the processing step for the current sample. The generating step generates a static magnetic field which is substantially homogeneous over a length of the transport path so that each sample is exposed to the static magnetic field for a predetermined period of time before it reaches the interrogation zone.
A further aspect of the invention is directed to an apparatus for determining an indication of the mass of a sample. The apparatus includes a signal generator operable to generate a non-uniform electric field within an interrogation zone for interacting with a sample located within the interrogation zone, a sensor operable to sense nuclear quadrupole resonance signals generated by the interaction of the sample with the non-uniform electric field and for outputting a signal in dependence thereon, a memory operable to store predetermined calibration data for at least one similar sample of known mass, which calibration data relates the mass of the at least one similar sample to the corresponding nuclear quadrupole resonance signal output by the sensor; and a comparator operable to compare the nuclear quadrupole resonance signal output by the sensor with the calibration data to provide the indication of the mass of the sample.